Butane, isobutane, propane, and other hydrocarbons were commonly used as refrigerants prior to World War II. The introduction of the family of FREON.RTM. fluorocarbon products in the early 1930s provided nonflammable, nontoxic, and what were believed to be environmentally safe substitute refrigerants for hydrocarbons. Fluorocarbons largely supplanted hydrocarbons as refrigerants of choice in most applications following World War II. Hydrocarbons are still in use today in special low temperature refrigeration systems (-100 degree Fahrenheit) due to the relatively high boiling points of fluorocarbons.
Certain chlorine containing fluorocarbon refrigerants, known as chlorofluorocarbons (CFC's), have been causally linked to the well-documented depletion of the earth's ozone layer. The Montreal Protocol and the United States Environmental Protection Agency EPA) have thus called for a phase out of the use of the CFCs that are known to be contributing to the degradation of the environment, and specifically to ozone layer depletion. Dichlorodifluoromethane (CCl.sub.2 F.sub.2), also known as CFC-12, Refrigerant-12, or simply R-12, is one of the most commonly used CFC refrigerants in automobile air conditioners and elsewhere. It is also the CFC refrigerant with the highest ozone depletion potential of any known refrigerant. R-12 has an "ozone depletion units" (ODU) measure of 1.0, and serves as the yardstick of ozone depletion potential against which all other refrigerants are measured.
New automobile air conditioners built in 1989 consumed 20 million pounds of R-12. An additional 80 million pounds of R-12 were consumed that year in replenishing the R-12 refrigerant that leaked from existing automobile air conditioners. Leaking of R-12 from automobile air conditioning systems is in fact a major source of the R-12 that escapes into the atmosphere each year.
Since the discovery in the 1970's that CFC refrigerants escaping into the atmosphere were depleting the earth's ozone layer, many companies have spent large sums of money trying to develop a non-toxic, nonflammable replacement for R-12 that could be "dropped into" existing automobile air conditioning systems as a substitute for R-12 without requiring any equipment changes. To date, no such "drop in" substitutes for R-12 have been announced. Consequently, the automobile industry plans to develop and market new automobile air conditioning systems by the 1995 model Year that use an ozone safe refrigerant, tetrafluoroethane (CH.sub.2 FCF.sub.3), also known as, FC-134a, Refrigerant-134a, or simply R-134a. Fortunately, R-134a has an ozone depletion factor (ODF) of zero. Unfortunately, R-134a cannot be drop-in substituted for R-12 in existing air conditioning systems due to compressor lubrication problems inherent in the use of R-134a in present systems, the inadequacy of the hoses used in present systems to handle R-134a, and the necessity of using a larger compressor than is now in use with R-12 refrigerant to Properly utilize R-134a.
Most automobiles that will be built through the 1994 model Year will still require the use of an R-12 refrigerant, or an acceptable drop-in substitute. With the environmental efforts to phase out, or ban, the use of ozone-depleting CFC's gaining momentum, it appears that an R-12 drop-in substitute for use in existing air conditioning systems must be found.